How to fit the axis title with two lines in R?

Question

I made one graph with 'two line' y-axis title using the code ylab(expression(paste()

Genotype <- c("CV1","CV2","CV1","CV2")
Category<- c("GN","GN","AGW","AGW")
mean <- c(1.47,1.66,0.98,0.93)
se<- c(0.10,0.20,0.03,0.06)
DataA<- data.frame(Genotype,Category,mean,se)
DataA


ggplot(data=DataA, aes(x=Genotype, y=mean, fill=Category))+
  geom_bar(stat="identity",position="dodge", width = 0.7) + 
  geom_errorbar(aes(ymin= mean-se, ymax=mean + se), position=position_dodge(0.7),
                width=0.2, size=1) +
  scale_fill_manual(values= c ("Dark gray", "Cadetblue")) + 
  scale_y_continuous(breaks = seq(0,2,0.2), labels = scales::percent, limits = c(0,2)) +  
  geom_hline(yintercept=1, linetype="dashed", color = "Dark red", size=1.5) + 
  xlab("Cultivar") +
  ylab(expression(paste("Value of thinning treatment \n relative to unthinning treatment"))) +
  theme(axis.title = element_text (face = "plain", size = 15, color = "black"),
        axis.text.x = element_text(size= 15),
        axis.text.y = element_text(size= 15),
        axis.line = element_line(size = 0.5, colour = "black"))+ 
  windows(width=7, height=5)

The y-axis title was divided into two lines, but the whole title was not fitted inside the graph. Even though I adjust the width of graph size, it was not applied to the axis title.

Could you tell me how to fit the whole y-axis title inside the graph well, maintaining the size of axis title (i.e. font size= 15)?

Thanks,

Answer 1

One way would be to adjust the margins giving more space to the left.

library(ggplot2)

ggplot(data=DataA, aes(x=Genotype, y=mean, fill=Category))+
  geom_bar(stat="identity",position="dodge", width = 0.7) + 
  geom_errorbar(aes(ymin= mean-se, ymax=mean + se), position=position_dodge(0.7),
                width=0.2, size=1) +
  scale_fill_manual(values= c ("Dark gray", "Cadetblue")) + 
  scale_y_continuous(breaks = seq(0,2,0.2), labels = scales::percent, limits = c(0,2)) +  
  geom_hline(yintercept=1, linetype="dashed", color = "Dark red", size=1.5) + 
  xlab("Cultivar") +
  ylab(expression(paste("Value of thinning treatment \n relative to unthinning treatment"))) +
  theme(axis.title = element_text (face = "plain", size = 15, color = "black"),
        axis.text.x = element_text(size= 15),
        axis.text.y = element_text(size= 15),
        axis.line = element_line(size = 0.5, colour = "black")) + 
  theme(plot.margin=unit(c(1,0.5,0.5,1.2),"cm"))